1. Field of the Invention
The present invention relates generally to an optical fiber designed to compensate for chromatic dispersion, and more particularly to a dispersion compensating optical fiber designed to provide superior compensation over a specified wavelength band.
2. Technical Background
Dispersion compensation techniques in telecommunications systems or spans have been used successfully. One useful dispersion compensation technique is where the total dispersion (also called chromatic dispersion) of a transmission span is compensated for by an appropriately designed (generally having a negative dispersion at 1550 nm) dispersion compensation optical fiber (a so-called dispersion compensating fiber). The dispersion compensating fiber is generally wound onto a spool and is housed in a dispersion compensation module. The dispersion compensating module is inserted into the transmission span at an access point, such as at the end of the span to compensate for the accumulated dispersion of the span.
Another dispersion compensation scheme involves the use of both positive and negative dispersion fibers in the cables of the span (a so-called dispersion managed cable). Each cable may contain both positive and negative total dispersion waveguide fibers, or the span can be formed using cables having only positive dispersion together with cables having only negative dispersion.
In yet another dispersion compensation technique, the dispersion compensating fiber exhibits a total dispersion and a total dispersion slope, both of which effectively mirror that of the transmission fiber. That is, the ratio of total dispersion to the total dispersion slope, referred to as kappa, is identical (or near identical) for the transmission fiber and the dispersion compensating fiber. Matching kappas of the two fibers helps improve compensation across the desired wavelength band.
Optical transmissions systems are currently designed with the goal of providing residual dispersion across a representative span that is very low within an operating wavelength band. However, new dispersion compensating fiber designs are continuously being sought after that can further reduce residual dispersion (defined herein as one half of the difference between the maximum and minimum dispersion across the wavelength band of interest for a 100 km length of transmission fiber being compensated).
There is, therefore, a need for a dispersion compensating fiber that provides low residual dispersion in systems operating over a specified wavelength band, and in particular, a need for dispersion compensating fibers that exhibit a low kappa and large effective area.